L-3-Phosphoglyceric acid,formed by ribulose-1,5-bisphosphate carboxylase,is the primary substrate for photorespiration: Experimental test of a hypothesis

Preparations of RuBP carboxylase are shown to carry out an oxygen dependent decarboxylation of L-3-phosphoglyceric acid. The product of this reaction is probably phosphoglycollate. L-3-phosphoglyceric acid, formed by RuBP carboxylase is therefore proposed to be the primary substrate for photorespiration.     

A crustacean compound eye adapted for low light intensities (Isopoda)

Summary The optical performance of the apposition compound eye of the marine isopodCirolana borealis Lilljeborg (Crustacea) was investigated. The ommatidia comprise large lenses (diam. ca. 150 m), spherical crystalline cones and hypertrophied rhabdoms. The 7 rhabdomeres are fused distally and open proximally. We have designated this rhabdom type as semifused. Distal pigment cells screen neighbouring ommatidia, and a well developed reflecting pigment layer surrounds the rhabdom. The focal length was determined in situ and refractive index measurements, raytracings, and eye mappings were made. The focus was found to lie well below the distal rhabdom tip. A theoretical acceptance function was constructed and a 50% acceptance angle of 45 ° was estimated. The eye parameter (p, according to Snyder 1977) of different ommatidia was between 44 and 14. This together with the anatomy demonstrate an optimation to extremely low light intensities. TheCirolana eye provides an example where acuity is sacrificed for the eye to be able to see at the low light intensities of the inhabitat.The investigation has been supported by a grant from the Swedish Natural Science Research Council (grant no. 2760-103). Our thanks are due to the staff of the marine biological station in Espegrend (Norway). The skilled technical assistance of Miss Inger Norling, Mrs. Rita Wallen, and Miss Maria Walles is gratefully acknowledged. And finally, we would like to express our deep appreciation to Professor Rolf Elofsson for constructive discussions and for his interest and encouragement throughout the investigation.     

Sympathetic nervous control of blood flow in the gills of the Atlantic cod,Gadus morhua

Summary The effects of sympathetic nerve stimulation, adrenaline and isoprenaline on the inflow pressure and efferent arterial and venous flow rates were studied in a cod gill preparation perfused at constant flow rate.The dominant effect of adrenaline was a reduced inflow pressure, accompanied by an increase in arterial flow and a decrease in venous flow. Isoprenaline also decreased the inflow pressure, but the changes in both outflow rates were small or absent.Sympathetic nerve stimulation gave arterial and venous flow changes comparable to the adrenaline effects, but the inflow pressure increased during nerve stimulation. Propranolol has little effect on the nerve responses, but phentolamine abolished or reversed the increase in inflow pressure, and also decreased or abolished the changes in outflow rates.The possible sites of action of the sympathetic fibres, and the distribution of adrenoceptors in the effector tissue is discussed. It is concluded that the main effect of sympathetic nerve stimulation is -adrenoceptor mediated, involving constriction of the arterio-venous pathway. The-adrenoceptor mediated control of total branchial vascular resistance may largely depend on circulating catecholamines.     

Linear and nonlinear models of the basilar membrane motion

A linear and a nonlinear transmission line model of the basilar membrane is described. The motion of the basilar membrane model has been simulated by numerical methods and compared with physiological data for several types of sound stimuli. It is shown that a linear model exhibits a frequency modulation in its impulse response that is in accordance with physiological data. The nonlinear model displays a sharpened frequency response for lower sound intensities. Futhermore, a nonlinear model explains why hearing damage imposed by short, high-intensity, sounds is extended to the low-frequency regions of the cochlea.     

STUDIES OF HAWAIIAN FRESHWATER AND SOIL ALGAE II. ALGAL COLONIZATION AND SUCCESSION ON A DATED VOLCANIC SUBSTRATE1,2

Spatial studies of colonization and succession of soil algae and chemical analyses of the various soils on the cinde cone of Kilauea Iki in Hawaii Volcanoes National Park, Hawaii are outlined. There is a positive correlation between the diversity and quantity of soil algae with nutrient levels and organic matter accumulation in each locale. Three distinct edaphic-biotic zones existing in this area are differentially revealed by the soil chemical composition, quantity and diversity of soil algae, and as evident variations in higher plant growth and colonization. Varying colonization and successional phases of higher plant growth around standing and fallen tree snags killed by volcanic activity also reflect variations in the soil algal flora. These variations appear largely as a function of differential water interception, absorption, and retention as well as differential accumulation of organic matter, and the initiation of various biogeochemical cycles.     

The use of a partition locus to increase stability of tryptophan-operon-bearing plasmids in Escherichia coli

The stability of different derivatives of plasmid vectors pBR322 and pACYC184 carrying the tryptophan operon of Escherichia coli was monitored in various media. It was found that in the absence of any special selective pressure, all plasmids were lost from the culture. The stability varied depending both on the orientation of the inserted tryptophan fragment and the growth media used. The pBR322::trp+ plasmids were lost at an average frequency of 0.3 to 0.8% per cell generation, while the pACYC184::trp+ plasmid was lost at a rate higher than 5%. In all cases the whole plasmid was lost at a rate higher than 5%. In all cases the whole plasmid was lost, indicating a high stability of the plasmid::cloned DNA as such. To increase the stability of the cloning vectors, the partition locus of plasmid pSC101 was added to both the pBR322::trp+ and pACYC184::trp+ plasmids. The addition of this gene increased the replicon stability at least 3- to 10-fold, with the pBR322::trp+-par+ plasmids being the most stable. Also in this case, the stability was dependent on the plasmid type and on the growth medium. In no case was there a discoordinate loss of the antibiotic-resistance and tryptophan genes from the vectors.     

Gene fusion vectors based on the gene for staphylococcal protein A

Two plasmid vectors, containing the gene coding for staphylococcal protein A and adapted for gene fusion, have been constructed. These vectors will allow fusion of any gene to the protein A gene, thus giving hybrid proteins which can be purified, in a one-step procedure, by IgG affinity chromatography. As an example of the practical use of such vectors, the protein A gene has been fused to the lacZ gene of Escherichia coli. E. coli strains containing such plasmids produce hybrid proteins with both IgG binding and β-galactosidase activities. The hybrid protein(s) can be immobilized on IgG-Sepharose by its protein A moiety with high efficiency without losing its enzymatic activity and they can be eluted from the column by competitive elution with pure protein A. The fused protein(s) also binds to IgG-coated microtiter wells which means that the in vivo product can be used as an enzyme conjugate in ELISA tests.     

Activation of human T lymphocytes by 12-O-tetradecanoylphorbol-13-acetate: role of accessory cells and interaction with lectins and allogeneic cells

Stimulatory effects of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) on human T lymphocytes have been investigated. TPA was found to stimulate highly purified T cells (obtained by a three-step isolation procedure involving plastic adherence, nylon wool passage and Ig-anti-Ig column passage) in the absence of accessory cells (stimulation index of 5 to 10), whereas phytohemaglutinin (PHA) and concanavalin A (Con A) did not. This response was, however, increased by the addition of autologous adherent cells. Addition of TPA, but not adherent cells, induced T-cell proliferation in response to the nonmitogenic lectin, wheat germ agglutinin (WGA), while both adherent cells and TPA restored T-cell proliferation to mitogenic lectins such as PHA and Con A. Furthermore, TPA greatly increased the mixed-lymphocyte response of purified T cells to otherwise nonstimulating allogeneic cells such as T lymphocytes or tumor cells from some patients with chronic lymphocytic leukemia. These results suggest that TPA can directly act on human T cells to render them reactive to a variety of stimuli.     

Kinetic characterisation of the enzymatic activity of the eEF-2-specific Ca2(+)-and calmodulin-dependent protein kinase III purified from rabbit reticulocytes.

The Ca2(+)-and calmodulin-dependent protein kinase III, which specifically phosphorylates the eukaryotic elongation factor 2 (eEF-2), has been purified to apparent homogeneity from the post-ribosomal fraction of rabbit reticulocytes by an efficient four-step method. The method results in a more than 4000-fold purification of the enzyme. SDS-gel electrophoresis showed that the purified kinase contained only one polypeptide with the apparent molecular mass of 90 kDa. The kinase activity was associated with the 90-kDa protein as shown by analyzing the phosphorylating activity of SDS gel electrophoretically purified protein electroblotted to nitrocellulose membranes. The purified kinase was dependent on Ca2+, Mg2+ and calmodulin for activity. Kinetic analysis of the phosphorylation reaction indicates that the turnover number of the kinase was approximately 1 s-1. The Km for the two substrates ATP and eEF-2 was calculated to be approximately 100 microM and 10 microM, respectively. The activity of the kinase was competitively inhibited by cAMP. The inhibition constant Ki (0.5 mM) was found to be in the same order of magnitude as that calculated for the competitive product inhibition caused by ADP. GTP was ten-times less efficient as competitor, indicating that the kinase had a preference for adenosine nucleotides. Phosphorylation of eEF-2 did not interfere with the diphtheria-toxin-catalysed ADP-ribosylation of the factor nor did ADP-ribosylation inhibit phosphorylation.